Storing contextual information in UIActionSheet - ios

Question

When creating a UIActionSheet to prompt a user to delete an item from a list, I currently have to maintain the deleted item (or at least its index in the list) as an instance variable in my view controller:
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
if ([indexPath row] == 4) {
// Delete button pressed
_deletingItemIndex = [indexPath section];
UIActionSheet actionSheet = ...
}
}
Then when the UIActionSheet closes, if the user decided to delete the item, I have to reference that _deletingItemIndex variable, then set it to -1 or some other nil value.
What I would like to do, is maintain either the deleting item, or its index, in the actual UIActionSheet without needing to subclass UIActionSheet.
I find it strange that the delegate method for UIActionSheet provides the sheet to the delegate, but you can't store any contextual information (not even a dictionary) in the sheet itself.

Answer 1

There are quite a few categories out there for adding block-based dismiss handlers to UIActionSheet and UIAlertView now. I personally use Mugunth Kumar's UIKitCategoryAdditions.
This would let you do the following...
[UIActionSheet actionSheetWithTitle:#"Hooray" message:#"Blocks Are Awesome!" buttons:#[...] showInView:self onDismiss:^(int buttonIndex) {
//Now you have access to all your local variables here!
} onCancel:^{
//And here!
}];

Answer 2

You should use objc_setAssociatedObject()
Have a look at http://darkdust.net/writings/objective-c/attaching-objects for some code.

Answer 3

UIActionSheet is a system object which should only be concerned with presenting a user with choices and getting a button index out.
Using an instance variable of view controller also doesn't make sense, because this isn't really a state of view controller, but rather of a current action which started existing the moment user started deleting.
The correct pattern, thus, is to create a new object, save information there, and use as a delegate:
MyDeletionAction *action = [MyDeletionAction actionWithIndex:[indexPath section]];
UIActionSheet actionSheet = ...
actionSheet.delegate = action;
...
and somewhere else, define MyDeletionAction as a class implementing the delegate protocol.
An added bonus of this approach is that you can take the code out of your view controller into separate classes, which is a good thing. Moreover, it's likely that your MyDeletionAction, MyInsertionAction etc. will share some common code.
Perhaps even the presence of action sheet should be an implementation detail of your action. For example, what if you provide an option to delete without confirmation?
Note also that in this approach someone should retain an action object, for example by object retaining itself until the action is fully completed, or by using a VC instance variable for this purpose:
self.lastAction = [MyDeletionAction actionWithIndex:[indexPath section]];
[self.lastAction start];
This also allows you to remember the state of last action for possible postprocessing.
start here appears because my actions usually have this kind of inheritance: MyDeletionAction <- MyAction <- NSOperation. Your mileage may vary.